Process of treating hardboard surfaces



Oct. '2, 1962 R. E. GRISSOM ET AL 3,056,718

PROCESS OF TREATING HARDBOARD SURFACES Filed June 29, 1959 N M R0 05 mm R E s e T R E B o R WILLIAM A SAUMS BY 6 i 7 ATTORNEY f a i...

tates The present invention relates to the production of lignocellulose hardboard sheet articles. More particularly, the invention relates to the production of hardboard having two smooth surfaces characterized by their freedom from unsightly defects and by their improved hardness, paint hold-out, and the like properties.

The manufacturers of hardboard have long engaged in the production of sheet articles having two smooth surfaces. Usually the hydrolyzed fiber has been felted into a wet lap which was then dried to substantial dryness in a conventional sheet drier. The dried lap, containing little or no moisture, was then consolidated under heat and pressure in a multi-platen press. One outstanding prior art method has been described and claimed in US. Patent No. 2,120,137 to Mason. In that process, hydrolized lignocellulose was formed into a wet lap on the forming screen of a Fourdrinier machine. After drying, the lap was pressed at about 400-500 F. under about 1,000 psi. pressure to obtain a final product having a specific gravity in excess of 1.0.

All of the prior art wet forming processes, however, were subject to one serious deficiency. Subsequent to formation of a wet lap, the lap was traveled between pressure rolls to remove as much water as possible. A top wire screen was employed in this step of the process. Therefore, both surfaces of the lap were imprinted with the screen design. Additionally, the seams of the screens were deeply imprinted on the lap surfaces. In the case of the top wire screen, which was about 40-50 feet long, this flaw obviously appeared very frequently. The screen marks persisted through the drying operation and have always been present in the finished sheet articles. Inasmuch as the products have normally been produced in 16 foot lengths, the deep seam mark of the top wire screen has been present in about one of every three boards. While the general screen impressions have been undesirable, the seam marks could not be tolerated. This necessitated cutting the board into shorter lengths and discarding the unsightly portion. The fault has been present in all prior art processes and has presented hardboard producers with a major problem for a period of many years.

It is a primary object of the present invention to provide a simple method for eliminating all screen marks from hardboard sheet articles having two smooth surfaces.

It is another object of the invention to provide a method for producing such hardboard sheet articles having improved surface physical properties.

Other objects of the invention will become apparent from the following detailed description. The description will be given with particular reference to the accompanying drawing in which the figure is a diagrammatic representation of a wet forming machine and conventional drier.

Briefly, the invention resides in the discovery that wire screen marks may be eliminated from the surfaces of wet formed hardboard sheet articles having two smooth surfaces by the application to the fibrous wet lap of a small amount of a naturally occurring non-conjugated vegetable drying oil. It has been found that where one or both of the lap surfaces are treated in this manner, all of the screen impressions are eliminated from the finally consolidated sheet products. The application of oil must be made prior to drying of the lap in order to obtain these 3,050,718 Patented Oct. 2, 1962 benefits. Unexpectedly, it was also discovered that hardboard sheets treated in this manner are characterized by surfaces which are considerably harder than conventional hardboard sheet surfaces and by improved paint hold-out properties as well as outstanding general improvement in appearance.

In carrying out the method of the invention, and with reference to the drawing, the numeral 10 represents the headbox of a conventional Fourdrinier-type board forming machine. The forming wire 12 of the machine travels over the suction box 14 and the bottom pressure rolls 16. As the lap 18 travels along the forming screen 12 it passes over the pressure rolls 16 and under the top pressure rolls 20. A top wire screen 22 travels around the top pressure rolls 20 and insures that the formation of the lap 18 is not disturbed during the pressure treatment. Thereafter the lap is cut into the desired lengths by the saw 24 and, as the individual wet laps proceed along the conveyor 26, a spray of oil is directed on one or both lap surfaces by means of a gang spray represented by the numeral 28. Thereafter the lap travels into the drier 30 which is normally a series of tiers through which heated air is blown to accomplish drying of the lap. Subsequent to passage through the drier 30, the lap is charged to the hydraulic press 32 where it is consolidated.

Prior to the present discovery, many different types of chemical compounds have been incorporated in the wet lap or sprayed on the surfaces thereof in attempts to improve the physical properties of the hardboard products. In every instance, however, there has been no improvement of the products. This failure has been due largely to the fact that the temperatures in the various zones of the drier range from about 750 F. to about 320 F. Accordingly, most additive compounds such as, for example, synthetic resins such as phenol-formaldehyde, furfural, ureaformaldehyde, melamine, and the like synthetic resins have been converted to their final infusible state during their passage through the drier. Quite unexpectedly it was discovered that the addition to the wet lap surface of about 0.1% to about 1.0% by Weight of a naturally occurring non-conjugated vegetable drying oil provides the above described improvements in the so-treated hardboard sheet articles. The specific drying oils which have been found to be usable in the novel method include linseed, soy bean, safilowe-r, and perilla oils. All of these oils are non-conjugated and therefore have slower drying characteristics than oils which are conjugated such as, for example, tung oil. While it is not known with exactness, it is believed that it is this slower drying characteristic which enables oils of this particular class to withstand the drying treatment temperatures without becoming completely polymerized prior to consolidation of the dried laps. In any event, subsequent to consolidation of the dried oil-treated laps, the so-treated sheet products are completely free from any wire screen impressions and the products are also improved as regards their physical characteristics. Use of less than about 0.1% of the selected oil does not produce the desired improvements. On the other hand, where more than about 1% of oil is employed, it is necessary to bake the finished sheet product to complete the polymerization of the oil and no further improvement is obtained. Additionally, greater amounts of oil tend to increase sticking of the sheets to the pressing plates during the consolidation treatment.

The treated laps, subsequent to drying, are consolidated into sheets having specific gravities which may range from about 0.8 to 1.2 depending on their ultimate use. For example, the laps may be pressed in a heated hydraulic press at about 1,000 psi. pressure and a temperature of about 240 C. to produce hardboard sheets having a specific gravity of 1.16. Using the same temperature but a with a pressure of only 200 p.s.i., the product has a specific gravity of 0.86. In all instances, the lap is held under very low pressure for about 3 minutes during which time the pressure is released periodically to allow escape of volatiles. Thereafter, the higher pressure is applied for about 0.5-2 minutes to effect the final consolidation of the sheet. Obviously other specific gravity products, Within the stated range, may be obtained by varying the pressing conditions.

It will therefore be appreciated that the novel process of the invention provides distinct advantages in the manufacture of hardboard sheet articles. The method is simple and does not add materially to the cost of production. Furthermore, it represents an economic advance by virtue of enabling the manufacture of hardboard free from surface defects while, at the same time, the products are characterized by improved physical properties.

We claim:

1. A process for producing a lignocellulose hardboard sheet article having two smooth surfaces characterized by freedom from screen marks which comprises forming an aqueous slurry of hydrolyzed lignocellulose fiber, felting a fibrous mat from said slurry, partially dewatering the fibrous mat by the application thereto of suction and pressure, applying at least one surface of the mat about 0.l%-1.0% by weight based on the dry weight of fiber of a naturally occurring non-conjugated vegetable drying oil, drying the treated mat to substantial dryness, and thereafter consolidating the dried mat under heat and pressure, said surface treatment with the drying oil substantially eliminating surface defects on the finished product.

2. In a process for producing a lignocellulose hardboard article having two smooth surfaces wherein hydrolyzed lignocellulose fiber is felted into a wet lap, dried by treatment with hot air at a temperature of about 300- 750 F., and then consolidated into a dense sheet, the step which comprises applying to at least one Surface of the wet lap about 0.1%1.0% by Weight based on the dry Weight of fiber of a naturally occurring non-conjugated vegetable drying oil, said surface treatment with the drying oil substantially eliminating surface defects on the finished product.

3. In a process for producing a lignocellulose hardboard article having two smooth surfaces wherein hydrolyzed lignocellulose fiber is felted into a Wet lap, dried by treatment with hot air at a temperature of about 300- 750 F., and then consolidated into a dense sheet, the step which comprises applying to at least one surface of Cit d the wet lap about 0.1%1.0% by weight based on the dry weight of fiber of linseed oil, said surface treatment with the drying oil substantially eliminating surface defects on the finished product.

4. in a process for producing a lignocellulose hardboard article having two smooth surfaces wherein hydrolyzed lignocellulose fiber is felted into a wet lap, dried by treatment with hot air at a temperature of about 300- 750 F., and then consolidated into a dense sheet, the step which comprises applying to at least one surface of the wet lap about 0.1%1.0% by weight based on the dry weight of fiber of soy bean oil, said surface treatment with the drying oil substantially eliminating surface defects on the finished product.

5. In a process for producing a lignocellulose hardboard article having two smooth surfaces wherein hydrolyzed lignocellulose fiber is felted into a wet lap, dried by treatment with hot air at a temperature of about 300- 750 F., and then consolidated into a dense sheet, the step which comprises applying to at least one surface of the wet lap about 0.1%1.0% by weight based on the dry weight of fiber of safilower oil, said surface treatment with the drying oil substantially eliminating surface defects on the finished product.

6. In a process for producing a lignocellulose hardboard article having two smooth surfaces wherein hydrolyzed lignocellulose fiber is felted into a wet lap, dried by treatment with hot air at a temperature of about 300- 750 F., and then consolidated into a dense sheet, the step which comprises applying to at least one surface of the wet lap about 0.l%1.0% by weight based on the dry weight of fiber of perilla oil, said surface treatment with the drying oil substantially eliminating surface defects on the finished product. 

1. A PROCESS FOR PRODUCING A LIGNOCELLULOSE HARDBOARD SHEET ARTICLE HAVING TWO SMOOTH SURFACES CHARACTERIZED BY FREEDOM FROM SCREEN MARKS WHICH COMPRISES FORMING AN AQUEOUS SLURRY OF HYDROLYZED LIGNOCELLULOSE FIBER, FELTING A FIBROUS MAT FROM SAID SLURRY, PARTIALLY DEWATERING THE FIBROUS MAT BY THE APPLICATION THERETO OF SUCTION AND PRESSURE, APPLYING AT LEAST ONE SURFACES OF THE MAT ABOUT 0.1%-1.0% BY WEIGHT BASED ON THE DRY WEIGHT OF FIBER OF A NATURALLY OCCURING NON-CONJUGATED VEGETABLE DRYING OIL, DRYING THE TREATED MAT TO SUBSTANTIAL DRYNESS, AND THEREAFTER CONSOLIDATING THE DRIED MAT UNDER HEAT AND PRESSURE, SAID SURFACE TREATMENT WITH THE DRYING OIL SUBSTANTIALLY ELIMINATING SURFACE DEFECTS ON THE FINISHED PRODUCT. 